Compressions numbers. Head gasket failure?

[m3_sancho]

Hi guys,

3 weeks ago I did a random compression test since I was replacing the plugs.

Cyl1: 162 PSI
Cyl2: 157 PSI
Cyl3: 164 PSI
Cyl4: 162 PSI
Cyl5: 147 PSI
Cyl6: 150 PSI

The vehicle starts fine, drives fine, doesn't throw codes. However Cyl5. and Cyl6 make me think of an early sign of Head Gasket Failure since the numbers are really close on both cylinders. One thing confirms me in this is a ping/rattle at around 3k when the vehicle is cold. I heard that the very first time yesterday going home after work. It wasn't there in the morning though. Came very suddenly.
What do you guys think? Am I right suspecting the Head Gasket?

UPDATE 05.05.2025
Finally pulled the head off last week. I wasn't driving the vehicle for over 1 year because suspected the head gasket fail. Good thing I didn't. Failed between cyl 5 and 6. Apparently I caught it very early thanks to the compression check and audible ping I heard couple of times and never drove the vehicle after that.

[EthanolTurbo]

Doesn't look too bad but the head gasket failure is very gradual so it can creep up on you. How many miles are on the engine?

[Kdubski]

When my head gasket failed @112k miles (had the ticking/rattling sound under load) my numbers where:

• Cyl 1 - 160
• Cyl 2 - 155
• Cyl 3 - 165
• Cyl 4 - 125
• Cyl 5 - 110
• Cyl 6 - 165

I'll find pictures of the burn through and attach them below.

[m3_sancho]

Doesn't look too bad but the head gasket failure is very gradual so it can creep up on you. How many miles are on the engine?

It has around 123k miles.

[sapote]

he vehicle starts fine, drives fine, doesn't throw codes. However Cyl5. and Cyl6 make me think of an early sign of Head Gasket Failure since the numbers are really close on both cylinders.

Do a leak-down test to confirm if it's a burnt gasket.

[tlow98]

Do a leak-down test to confirm if it's a burnt gasket.

This. If it’s leaking to the adjacent cylinder it will be very obvious. And you’ll want to move fast as resurfacing the block means an engine rebuild.

leak down and assess.

[m3_sancho]

This. If it’s leaking to the adjacent cylinder it will be very obvious. And you’ll want to move fast as resurfacing the block means an engine rebuild.

leak down and assess.

What do you mean by engine rebuild? Is resurfacing the head already an engine rebuild?

[WestBankM4]

What do you mean by engine rebuild? Is resurfacing the head already an engine rebuild?

Surfacing the head is simply that, usually done when replacing the head gasket. If the iron block is scored enough, then I believe tlow98 is stating, you're in for an engine rebuild. Your symptoms doesn't sound as bad as mine nor the compression numbers but the pinging means there's a break in the headgasket and the hot gasses are passing between cylinder walls 5 and 6.

You'll want to tackle the problem sooner than later.

[Icecream]

Surfacing the head is simply that, usually done when replacing the head gasket. If the iron block is scored enough, then I believe tlow98 is stating, you're in for an engine rebuild. Your symptoms doesn't sound as bad as mine nor the compression numbers but the pinging means there's a break in the headgasket and the hot gasses are passing between cylinder walls 5 and 6.

You'll want to tackle the problem sooner than later.

Exactly, ask me how I know. Stop driving or its full tear down.

[tlow98]

Yes, but your numbers aren’t really that low. But if you want to know 100% leak down it is.

[ChapterM3]

m3_sancho - Reading your first post makes me think about what's been going on with my car, and how it started. I had a random misfire that started randomly only at startup, and that's what led to an entire thread which you can read here. After a compression test and leakdown my head gasket is the main suspect between 5-6. The last time I drove it before Anri picked it up I heard a ping right at 2.5-3k, which I never heard before, and that sounds like what you're describing as well. I'd wonder what Anri might say about your numbers between 5 and 6.

https://nam3forum.com/forums/forum/main-forum/e46-2001-2006/228970-the-m3-is-getting-the-anri-build-treatment-blown-headgasket-to-build-thread

[m3_sancho]

Let's say I caught it in time and it needs only a head gasket replacement. Can I slap just a new gasket on or would I need to skim the head regardless?

[ChapterM3]

From everything that I've read up on, and the people that I've spoken with, you need to skim the head regardless to provide a new surface for the gasket to seal correctly to. With the amount of work that goes into taking the head off you might as well do other maintenance items that are in there as well, and at the end of the day once it's pulled you'll really see what's going on with the motor. If you look at my thread I posted in my previous post you'll see the comments back and forth about what you might find when pulling the head. Not saying it's the case or to discourage you, only saying that you really only know what's going on once it's actually off and there might be more work that is needing to be done to say the block/cylinders, etc.

[sapote]

Let's say I caught it in time and it needs only a head gasket replacement. Can I slap just a new gasket on or would I need to skim the head regardless?

If the head surface has no bunt groove (between the cylinders) and not warp (check with straight edge) then I would clean it up and no need to machine to take off a thin layer.
But in this case, with the hot combustion gas leaking through, I think it had burnt through so check it carefully to see if it needs machining.

[m3_sancho]

Updated the first post. Head gasket failed.